Technical Field
The subject matter disclosed herein relates to methods and systems for managing open circuit voltage checks of energy storage modules in an energy storage system.
Discussion of Art
In certain battery systems, it may not be practical to sense voltage from every cell in a battery. Therefore, open circuit voltage (OCV) measurements are often a primary means of determining battery health and detecting the presence of cells that have failed to an electrical short. An OCV check may be manually performed by a technician on a battery module (energy storage module) to determine a number of cells in the battery module, if any, that have failed or are degraded. In energy storage systems having many battery modules, such as in an uninterruptable power supply (UPS) system for a telecommunications site or a server farm, for example, the ability to schedule and perform OCV checks on the battery modules may be limited. For example, manually checking OCV during system operation can be problematic since a battery module may need to be disconnected from a DC bus and discharged below a certain state-of-charge level before performing the OCV check. Battery modules used as backup typically spend almost all of their time connected to the system in a fully charged state. Therefore, system performance or availability can be compromised when performing an OCV check.
Brief Description
Systems and methods for managing open circuit voltage checks of energy storage modules in an energy storage system are disclosed. Embodiments of the present invention provide a controller of an energy storage system configured to schedule open circuit voltage checks for the energy storage modules, determine if conditions of an energy storage module, and of the overall energy storage system, are favorable for performing an open circuit voltage check, and defer an open circuit voltage check if at least one condition is not favorable. The controller is further configured to abandon an open circuit voltage check in progress if one or more conditions of the overall energy storage system changes in a manner that is unfavorable for continuing with the open circuit voltage check.
In one embodiment, a method is provided. The method includes deferring an open circuit voltage check of a battery module in a battery system when the battery module is in operational service or when the battery module is scheduled to be in operational service during a designated period for the open circuit voltage check. The method further includes initiating the open circuit voltage check and monitoring for a battery system discharge during the open circuit voltage check. The method also includes reconnecting the battery module to a direct current (DC) bus of the battery system and deferring the open circuit voltage check when the battery system discharges during the open circuit voltage check. The method may include determining if a state-of-charge of the battery module is within a designated state-of-charge range for performing the open circuit voltage check, and when the state-of-charge is not within the designated state-of-charge range, disconnecting the battery module from the DC bus and discharging the battery module to the designated state-of-charge range. The method may include determining if a state-of-charge of the battery module is within a designated state-of-charge range for performing the open circuit voltage check, and when the state-of-charge is within the designated state-of-charge range, disconnecting the battery module from the DC bus and waiting for the battery module to depolarize. The method may include determining if a state-of-charge and a temperature of the battery module are respectively within a designated state-of-charge range and a designated temperature range for performing the open circuit voltage check, and when the state-of-charge is not within the designated state-of-charge range and the temperature is within the designated temperature range, disconnecting the battery module from the DC bus and discharging the battery module to the designated state-of-charge range. The method may include determining if a state-of-charge and a temperature of the battery module are respectively within a designated state-of-charge range and a designated temperature range for performing the open circuit voltage check, and deferring the open circuit voltage check to a later time when the temperature is not within the designated temperature range. The method may include determining if a state-of-charge and a temperature of the battery module are respectively within a designated state-of-charge range and a designated temperature range for performing the open circuit voltage check, and when the state-of-charge is within the designated state-of-charge range and when the temperature is within the designated temperature range, disconnecting the battery module from the DC bus and waiting for the battery module to depolarize. The method may include measuring an open circuit voltage of the battery module, and reporting a value of the open circuit voltage to a controller of the battery system. The method may include determining that one or more cells within the battery module have failed or are degraded, based on the reported open circuit voltage value, and scheduling the battery module for maintenance.
In one embodiment, a battery system is provided. The battery system includes a plurality of energy storage modules operably couplable/decouplable to a direct current (DC) bus, wherein the energy storage modules include respective module management systems, and a controller, in communication with the module management systems, that is operable to selectively initiate coupling/decoupling of the energy storage modules to the DC bus, and to schedule an open circuit voltage check of at least one energy storage module of the plurality of energy storage modules, determine if the at least one energy storage module is to be coupled to the DC bus, and defer the open circuit voltage check to a later time when the at least one energy storage module is to be coupled to the DC bus. The controller may be further operable to determine if a system discharge is detected during the open circuit voltage check of the at least one energy storage module, and couple the at least one energy storage module to the DC bus of the battery system when the system discharge is detected during the open circuit voltage check and defer the open circuit voltage check to a later time. The controller may be further operable to determine if a state-of-charge of the at least one energy storage module is within a designated state-of-charge range for performing the open circuit voltage check, and when the state-of-charge is not within the designated state-of-charge range, command that the at least one energy storage module be decoupled from the DC bus and discharged to the designated state-of-charge range. The controller may be operable to determine if a state-of-charge of the at least one energy storage module is within a designated state-of-charge range for performing the open circuit voltage check, and when the state-of-charge is within the designated state-of-charge range, command that the at least one energy storage module be decoupled from the DC bus and depolarized. The controller may be operable to determine if a state-of-charge and a temperature of the at least one energy storage module are respectively within a designated state-of-charge range and a designated temperature range for performing the open circuit voltage check, and when the state-of-charge is not within the designated state-of-charge range and the temperature is within the designated temperature range, command that the at least one energy storage module be decoupled from the DC bus and discharged to the designated state-of-charge range. The controller may be operable to determine if a state-of-charge and a temperature of the at least one energy storage module are respectively within a designated state-of-charge range and a designated temperature range for performing the open circuit voltage check, and defer the open circuit voltage check to a later time when the temperature is not within the designated temperature range. The controller may be operable to determine if a state-of-charge and a temperature of the at least one energy storage module are respectively within a designated state-of-charge range and a designated temperature range for performing the open circuit voltage check, and when the state-of-charge is within the designated state-of-charge range and when the temperature is within the designated temperature range, command that the at least one energy storage module be decoupled from the DC bus and depolarized. At least one of the module management systems of the at least one energy storage module may be operable to measure an open circuit voltage of the at least one energy storage module, and report a value of the open circuit voltage to the controller. The controller may be operable to determine that one or more cells within the at least one energy storage module have failed or are degraded, based on the reported open circuit voltage value, and schedule the at least one energy storage module for maintenance.
In one embodiment, a battery system is provided. The battery system includes means for selectively initiating coupling/decoupling of at least one energy storage module to a direct current bus, means for scheduling an open circuit voltage check of the at least one energy storage module, means for determining if the at least one energy storage module is to be coupled to the direct current bus, and means for deferring the open circuit voltage check to a later time when the at least one energy storage module is to be coupled to the direct current bus. The battery system may further include means for determining if a system discharge is detected during the open circuit voltage check of the at least one energy storage module, and when a system discharge is detected during the open circuit voltage check, means for coupling the at least one energy storage module to the direct current bus and deferring the open circuit voltage check to a later time. In accordance with an embodiment, one or more of the means may be a set of non-transient instructions stored in a machine-readable medium that, when executed by a controller, cause the controller to perform the stated function of the means.
In one embodiment, a battery system is provided. The battery system includes coupler means for selectively initiating coupling/decoupling of at least one energy storage module to a direct current bus, schedule means for scheduling an open circuit voltage check of the at least one energy storage module, determination means for determining if the at least one energy storage module is to be coupled to the direct current bus, and deferral means for deferring the open circuit voltage check to a later time when the at least one energy storage module is to be coupled to the direct current bus. The determination means may include means for determining if a system discharge is detected during the open circuit voltage check of the at least one energy storage module, and the coupler means and the deferral means may include means for coupling the at least one energy storage module to the direct current bus and means for deferring the open circuit voltage check to a later time, respectively, when the system discharge is detected during the open circuit voltage check. In accordance with an embodiment, one or more of the means may be a set of non-transient instructions stored in a machine-readable medium that, when executed by a controller, cause the controller to perform the stated function of the means.
In one embodiment, a method is provided. The method includes disconnecting a battery module of a battery system from a direct current (DC) bus of the battery system, initiating an open circuit voltage check of the battery module and monitoring the DC bus for a battery system discharge during the open circuit voltage check, and reconnecting the battery module to the DC bus of the battery system and deferring the open circuit voltage check when the battery system discharges during the open circuit voltage check.
In one embodiment, a method is provided. The method includes scheduling an open circuit voltage check of a battery module in a battery system, if the battery module is in operational service at a designated time of commencing the open circuit voltage check according to the scheduling, or if the battery module is scheduled to be in operational service during a duration of the open circuit voltage check according to the scheduling, deferring the open circuit voltage check to a first time later than the designated time, subsequent to deferring the open circuit voltage check, initiating the open circuit voltage check at the first time and monitoring for a battery system discharge during the open circuit voltage check, and responsive to the battery system discharge occurring during the open circuit voltage check, reconnecting the battery module to a DC bus of the battery system and further deferring the open circuit voltage check to a second time later than the first time.